Sound absorbing micro-porous wall panel structures



May 1965 H. WILHELMI ETAL 3,182,747

SOUND ABSORBING MICRO-POROUS WALL PANEL STRUCTURES Filed Jan. 8, 1960 INVENTORS HANS WILHELMI WALTER NEUDERT BY WW ATTORNEY.

United States Patent 4 Claims. (31. 18133) This is a continuation-impart of the co-pending patent application Serial No. 500,186, filed April 8, 1955, now abandoned.

The present invention relates to sound absorbing devices. It is particularly concerned with arrangements comprising sound absorbing wall elements in the form of plates or foils having a perfiorated surface.

Many known sound absorbing panels have the disadvantage that .they lack a neat and pleasing appearance possessing a perforated and/or rough surface structure. Also, these panel-s become dusty very easily. Furthermore, they are generally sensitive to moisture and therefore cannot be washed. Furthermore, the painting of such panels is often difiicult, if not impossible, and they are generally inflammable.

In order to be able to absorb sound sufficiently, many known panels must be relatively thick and in practice are usually 1050 mm. thick. Consequently they are heaay. Also, owing to the low strength of the materials of which they are composed, these known panels are produced in small sizes only. For these reasons, the mounting of the panels involves a considerable expense.

It is one object of the present invention to avoid the drawbacks of the known sound absorbing panels and to provide a sound absorbing material with a neat and pleasing surfiace which can be washed, cleaned and painted.

It is a further object of the present invention to provide a material which does not require a large thickness and keeps down the Weight, so that comparatively large plates can be formed and easily handled and applied to walls and ceilings at low costs.

It is yet another object of the present invention, to provide sound absorbing panels which comprise a thin, hard and smooth micro-porous sound absorbing layer, with a thickness of preferably not more than 5 mm., which is self-supporting and mountable spaced apart from the adjacent wall and wherein the micro-porous structure is produced by a chemical process. The panel possesses an open micro-porous structure. Preferably the panel is composed of substantially non-inflammable material.

According to the present invention there is provided a sound absorbing sheet which is self-supporting, the thickness of the sheet being not greater than 5 mm, said sheet possessing an open microporous structure and an air flow resistance per square centimeter of 25 to 1000 g. cm.- sf Preferably the said sheet is composed of substantially non-inflammable material.

The new material has a low weight and this enables a simple mounting in finished buildings. It allows also a satisfactory combination of the sound absorbing arrangement with other equipment of engineering nature, for instance with radiation heating.

With these and other objects in view which will become apparent in the following detailed description, the present invention will be clearly understood in connection with the accompanying drawings, in which:

FIGURE 1 is a perspective tron-t view of a portion of a wall provided with the sound absorbing structure;

FIG. 2 is a sectional view of another embodiment of the sound absorbing structure; and

FIG. 3 is a sectional view of two other embodiments of the present invention.

FIG. 4 is a diagrammatic view of a coffered ceiling comprising sound absorbing plates according to the present invention.

.Referring now to the drawing, FIG. 1 shows a part of a wall 1 or a ceiling which may consist of masonry or the like. The wall 1 carries distancing pieces 2 in the form of boards or strips for holding a plate 3 having a thickness of about 1 mm, for instance. This plate 3 has a microporous structure so that the sound waves are absorbed by this device.

The sheets according to the present invention are selfsupporting over moderate areas, thus facilitating mounting. The sound absorbing sheets according to the vpresent invention thus possess greater mechanical strength than hitherto known sound absorbing panels, such as those of compressed fibres, which in general have little mechanical strength. The sheets according to the present invention are further preferably hard and smooth, enabling them to be readily washed. The absorption of sound by sheets according to the present invention is due to their open micro porous structures; the sheet thus has a structure providing many pores :or channels enabling air to pass from one side of the sheet to the other, the size of the pores or channels being such, however, as to cause damping of sound waves being transmitted therethrough. The sheet thus has very favorable air flow resistance which may be easily regulated.

The air flow resistance of thin laminar material can be measured in terms of the volume of air U, flowing through a given area A, of the material in unit time when there exists a given difference in air pressure AP, between the two sides of the material. :If U is measured in cubic centimeters per second and AP in dynes per square centimeter, the air flow resistance Ra of the sheet is given by the relationship:

If A, the area of the sheet, is in square centimeters, the

air flow resistance per square centimeter will be:

RaXA g. curs.-

The thickness of the sheet is not greater than 5 mm. and is preferably at least 0.5 mm.

.Thus, for example, a sound absorbing sheet according to the present invention having a thickness of 1 mm. can be made with an acoustic resistance comparable to a layer of 50 mm. thickness of sound absorbing material of known type com-posed of glass wool.

The sheet according to the present invention can be made of low weight which, combined with good mechanical strength enables simple mounting in a building.

The sheets according to the present invention may be made by a number of processes which are all based on the fact that under certain conditions micro-pores are pro duced by the changing state of aggregation of substances as they harden from the liquid to the solid state, through a gelatinous state, by shrinking and expansion during bardening, ifior example as frequently happens in polymeriza- "tion reactions.

In confiormity with one method tor instance, either a soluble or a 'dispersible hardenable substance is mixed with a fast evaporating solvent (to form a solution or disper sion) and one or more slowly evaporating non-solvents for the hardenable substance and the mixture is then hardened so that at first the solvent evaporates and then the non-solvent produces the micropores by slow evaporation during progressive hardening. For example, for this purpose a polyester resin, which can be an unsaturated branched hydroxyl and/ or carboxyl terminated of high molecular weight, is mixed thoroughly with a cyclohexa- 3 non-peroxide as hardener and a cobalt naphthenate as an accelerator. The viscosity of the polyester may be decreased by addition of a low percentage ofmonosoyrene. This mixture is diluted by an addition of a fast evaporating solvent for the resins such as methylene chloride, and, after a further addition of a slowly evaporating non-solvent such as ethylene-glycol which has a high boiling point, it is quickly heated between two plates separated by a small distance up to an oven temperature of, for instance, 160 C. (320 1 After a short hardening pe riod of 1 to 2 minutes, the two =plateswhich have been previously impregnated with :a separating substanceare removed and a thin sheet with open micro pores is obtained having the desired thickness. A similar effect may be obtained with other resins.

It is also possible to dissolve or disperse two hardenable substances which do not react with each other in a common solvent and to harden them, evaporating off the solvent :pa-rtly before and partly during the hardening process.

The production of a very thin sheet or of a sheet of greater strength particularly flex-ional strength, may be carried out by theme of fibers in loose or bound form as a filling medium or as carrier for the sheet. A fleece or a fabric may be combined with the above-mentioned mixture, while it is in liquid form and the mixture then hardened under pressure and heat. The ratio of the quantities of the various substances as well as the pressure depends on the desired porosity or on the intended air ilow resistance.

A further example for the production of a sound absorbing sheet according to the present invention will now be described. An inorganic fibre fleece derived from a sodium glass webbing is treated with potassium silicate, which has a high aflinity for this sodium glass, and is combined with a trace of antimony trioxide in a ratio depending on the desired porosity. Such inorganic iibre fleece may comprise gl-ass wool, stone-wool, slag-wool, asbestos fibres or metal-wool. -By the increase of the concentration of hydrogen ions (lowering'the pH value) caused by the addition of acidic. antimony trioxide silica gel is produced which combines with the webbing on account of the said high afiinity. By this change in the state of aggregation from a solution-fluid, through a gel, to a solid substance when pressure and heat are applied, the microporous structure is obtained as mentioned above, the temperature at which the process is carried out being such that little or no sublimation of the antimony trioxide takes place.

It is also possible to produce the micro-pores by employing additional soluble solid substances giving off gases during the hardening. The various methods of production may also be combined.

When it is intended to adjust exactly the sound absorption of a given installation the sheet when mounted may be coated or sprayed with a varnish or lacquer for example chlorinated rubber dissolved in methylene chloride to provide a top surface layer 3a which serves to close some of the open pores on the surface of the sheet. This step produces not only a decorative effect, for instance a unifiorm or specially attractive effect over the entire surface, but also a uniform fine adjustment of the sound dead ening efieet. This step may also be carried out befiore 'mounting the plates 3 on the wall 1, as on the ceiling.

If a colored effect is desired, coloring substances may be added to the various materials.

Referring now to FIG. 2 of the drawing though it is understood that the sound absorbing structure may be arranged in a large variety of ways, the arrangement disclosed in 'FIG. 2 comprises a sound pervious backing layer 4 carrying the sound absorbent sheet or foil 3. The backing layer 4 is' fastened directly to the wall 1'; Be-

. sides the arrangement shown in FIGS. 2 and 3, which show aflat sheet of the sound absorbing foil, it is also possible to use curved sheets ofthe foil or sheet. A particularly simple arrangement is obtained, when the sound absorb-' ing structure is formed during the production in such a manner that it contains means for fastening it spaced apart from the wall or ceiling. Such an arrangement is represented in FIG. 3. The box-like structure is formed with walls 5 having micro-pores to constitute. a sound absorbing sheet and with portions for fastening it to the wall or ceiling 1 with fastening means 7, for instance screws or nails. The second structure, disclosed likewise in FIG. 3, has a bent or curved sheet 6, secured to the wall '1 by similar fastening means 7. A ilat sound-absorbing sheet may be bent and fastenedbetween the bent portion thereof, or the sheet may be preformed in the shape of a cap or a part of a sphere. Smaller sheets may be arranged to form bays or a coffered ceiling. FIG. 4 shows sheets 8 and 9 which form a frame-like structure. The sheets may also be carried by other porous backing layers or :filigreedike supports which may be prefabricated.

The colored eifect referred to above, is brought about by adding inorganic color substances.

In order to obtain a white color, titan-dioxide, zincdioxide or zinc-sulfide is admixed to the basic material. In order to obtain yellow, red, brown or black colors, all iron-oxide colors may be used. In order to obtain a green color, chromium oxide and chromium oxide hydrate, respectively, is used. For obtaining a blue color effect, ultramarin is used. These colors may be applied individually or in mixtures thereof.

While we have disclosed several embodiments of the present invention, it is to be understood that these embodiments are given by example only and not in a limiting sense, the scope of the present invention being determined by the objects and the claims.

We claim:

1. A self-supporting independent sound absorbing sheet having a thickness ranging from at least about 0.5 mm. up to about 5 mm. and possessing an open micro-porous structure and an air flow resistance per square centimeter of 25 to 1000 g. cmr sr' said sheet being adapted to be mounted at a predetermined distance from a wall to operate as sound absorbing means.

2. The sheet, as set forth in claim 1, consisting substan tially of non-inflammable material.

3. The sheet, asset =fiorth in claim 1, wherein at least a part of the surface of said sheet is covered with a layer of a material selected from the group consisting of varnish and lacquer.

4. The sheet, as set forth in claim 1, which includes a sound permeable backing layer, supporting said sheet.

References Cited by the Examiner UNITED STATES PATENTS Re. 14,992 1 1/ 20 Sabine et al. 1,119,543 1'2/14 Sabine et al.

1,440,073 12/2 2 Guastavino. 1,790,938 2/ 31 Marcus. 1,8 67,549 7/ 32 Brockmeyer.

2,028,180 1/36 Arnold.

2,045,099 6/ 36 Pond. 2,067 ,31-2 1/37 Coryell, 2,170,102 8/ 39, Thompson 1 81-53 2,372,695 4/45 Taylor 181-33 2,390,262 12/ 45 Mazer. j 2,450,911 10/48 a Park et al.

7 2,502,016 3/ 50 Olson.

2,576,073 11/51 Kropa et al. 2,703,627 3 /55 DEustachio. 2,704,865 3/55 Siering. 2,779,429 1/57 Mazer. 2,789,095 4/ 5 7 Lindvig. 2,791,289 5/57 Proudfoot, et. a1. 2,797,201 6/57 Veatch et al.;

IJEO SMILOW, Primary Examiner. JOHN C. MCNAB, C. W. ROBINSON, Examiners; 

1. A SELF-SUPPORTING INDEPENDENT SOUND ABSORBING SHEET HAVING A THICKNESS RANGING FROM AT LEAST ABOUT 0.5 MM. UP TO ABOUT 5 MM. AND POSSESSING AN OPNE MICOR-POROUS STRUCTURE AND AN AIR FLOW RESISTANCE PER SQUARE CENTIMETER OF 25 TO 1000 G. CM.-2.S.-1, SAID SHEET BEING ADAPTED TO BE MOUNTED AT A PREDETERMINED DISTANCE FROM A WALL TO OPERATE AS SOUND ABSORBING MEANS. 